The characteristic of Aristotle’s philosophy, as compared with that of Plato, is, that while the latter gave free scope to his imagination, and, by his doctrine that we have ideas independent of the objects which they represent, opened a wide door to the dreams of mysticism—the latter was a close and strict observer of both mental and physical phenomena, avoiding all the seductions of the fancy, and following a severe, methodical, and strictly scientific course of inquiry, founded on data ascertained by experience. The truly philosophical character of his mind, and his calm and singularly dispassionate manner of writing, are not more remarkable than the vast extent both of his reading and of his original researches. His writings appear to have embraced nearly the whole circle of the theoretical and practical knowledge of his time, comprising treatises on logical, metaphysical, rhetorical, poetical, ethical, political, economical, physical, mechanical, and medical science. He likewise wrote on some parts of the mathematics; and, besides a collection of the constitutions of all the states known in his age, both Grecian and barbarian he made chronological compilations relating to the political and dramatic history of Greece. His works, however, though embracing so large an extent of subjects, were not a mere encyclopædia, or digest of existing knowledge; some of the sciences which he treated of were created by himself, and the others were enriched by fresh inquiries, and methodized by his systematic diligence. To the former belong his works on analytics and dialectics, or, as it is now called, logic; to the invention of which science he distinctly lays claim, stating that “before his time nothing whatever had been done in it.” Nearly the same remark applies to his metaphysical treatise. “But of all the sciences,” says Cuvier, “there is none which owes more to Aristotle, than the natural history of animals. Not only was he acquainted with a great number of species, but he has studied and described them on a luminous and comprehensive plan, to which, perhaps, none of his successors has approached; classing the facts not according to the species, but according to the organs and functions, the only method of establishing comparative results. Thus it may be said that he is not only the most ancient author of comparative anatomy, whose works have come down to us, but that he is one of those who have treated this branch of natural history with the most genius, and that he best deserves to be taken for a model. The principal divisions which naturalists still follow in the animal kingdom, are due to Aristotle; and he had already pointed out several which have recently been again adopted, after having once been improperly abandoned. If the foundations of these great labors are examined, it will be seen that they all rest on the same method. Everywhere Aristotle observes the facts with attention; he compares them with